Repair help for Vizio sound bar power supply

[rynomilner]

My sound bar suddenly quit working entirely (zero signs of life) the other day and now I'm trying to see if I can work out what went wrong.

I've narrowed it down to the power supply (MKL90W-02-C1), though I see no obvious places where the magic smoke has escaped and, upon powering the PSU, nothing gets warm to the touch. The rectification and initial smoothing seems to be fine, providing ~174 VDC (I'm in US). The output of the PSU board is supposed to be +24v and +5v. If I manually hook up my benchtop power supply and supply those voltages (supply points indicated in image) the entire thing works fine. So it seems to be somewhere between the "HOT" and "COLD" labeled sides of the board where something goes wrong. I don't measure a single point on the "COLD" side that is either 5v or 24v.

My main candidate is the big transformer-looking thing with the yellow plastic peeled off. The label shows MK BCK-32BK. The smaller one next to it is BCK-1609. I think they're from this eLemay company http://www.e-lemay.com/Product1.aspx?fid=1&sid=4

I don't understand what a transformer would be doing on an area of the board which is all DC, so maybe it's a filter or something? I don't really know what it is so I don't know how to test it.

Any ideas of what I should check?

[rynomilner]

Solved it! For future reference, the problem was capacitor C21. Didn't look like it was bulging, but replaced it anyway and works like a champ now.